The evaluation of the performance of self contained hydrodynamically lubricated bearings in DEM's has hitherto been a difficult task to perform. Oil rings mounted on a shaft in a bearing assembly are not readily accessible during operation of the DEM for close examination to determine how effectively the lubricating oil is being transferred to the bearing from the oil reservoir located in the bearing housing.
Because the rotation of the oil ring is reliant on frictional engagement between the shaft and oil ring mating surfaces, it is apparent that any disturbance which alters the coefficient of friction between the oil ring and the shaft will lead to increase slippage of the oil ring on the shaft with a resultant consequent decrease in the volume of lubricating oil delivered to the bearing.
It will be readily apparent that as the shaft speeds of DEM's are increased, the oil ring speed must increase with increasing shaft speed to the point where the oil film between the oil ring and the shaft causes the oil ring to begin to slip on the shaft because the drag force on the immersed portion of the oil ring constantly increases as the oil ring moves through the oil reservoir of the bearing. The shearing forces acting on the oil ring continue to increase while the driving force causing the ring to rotate remains relatively constant. At some point the driving force, tending to turn the oil ring, is largely dissipated in overcoming the shear forces of the oil ring moving through the oil in the bearing reservoir and the ring begins to slip.
Attempts to evaluate the effectiveness of this method of lubricating the bearings of DEM's have usually resorted to the visual observation of the rotation of an oil ring which has been suitably marked to enable the observer to count the rotations of the oil ring during operation of the DEM. The correlation between oil ring rotation and the amount of oil delivered to the bearing in a relationship which is relatively easy to establish by those skilled in the tribological art.